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Chapter 9: Waveguide Grating and dapplications Dr. Assoc. Prof. Yaocheng Shi yaocheng@zju.edu.cn Centre for Optical and Electromagnetic Research, Department of Optical Engineering, Zhejiang University
Waveguide Bragg Grating
Couple Mode Theory Contra-directional Coupler (See Lecture 4)
Couple Mode Theory
Couple Mode Theory
Couple Mode Theory
Couple Mode Theory
Bragg Grating Bragg Condition: 2 n m 0, m=1, =1234 2, 3, 2013/10/13 第二章平面介质光波导和耦合模理论 9
Uniform Bragg Grating 谐振峰两边有一些旁瓣 由于光栅两端折射率突变引起 F-P 效应导致的 旁瓣分散了光能量, 不利于其应用, 需进行旁瓣抑制
Apodized Bragg Grating 两端折射率分布逐渐递减至零, 消除了折射率突变, 从而使反射谱不存在旁瓣 高斯切趾 平均值为零的升余弦切趾
Chirped Bragg Grating 折射率调制幅度不变, 而周期沿光栅轴向变化, 反射谱宽增加 长波长 短波长
DFB 半导体激光器 DFB (Distributed Feedback) DFB 激光器的发射波长与光栅的周期 折射率相关 直接在半导体激光器的有源区制作波导布拉格光栅, 构成谐振腔, 且有源区和反馈区同为一体
DBR 波导激光器 DBR (Distributed Bragg Reflector) WBG 与有源区分离, 实现有源区和光栅区的独立控制 DBR 半导体激光器可获得比 DFB 半导体激光器更高的模式选择性, 获得稳定的单模运行 ;DBR 半导体激光器也是目前商用化最好的一种可调谐激光器
F-P-LD 与 DFB-LD 的纵模间隔 FP-LD DFB-LD
Sampled Grating Distributed Bragg Reflector (SG-DBR) FSR 1 FSR 2 FSR T f f f 腔 1 腔 2 级联腔 游标式级联腔 KFSR 1 =(K+1) FSR 2 FSR T = K FSR 1 =(K+1) FSR 2
Application: Filters X. Wang, et al. Opt. Exp., 20(14), (2012).
Application: Filters D. Kim, et al. Appl.Phys.Lett., 88, 071120, (2006).
Application: Filters W. Chuang, et al. Opt. Exp., 19(11), 10776-10788, 10788, (2011).
Application: Filters/OADM T. Chu, et al. Photon. Technol. Lett., 18(13), (2006).
Application: Reflectors/FP Cavities L G L c L T W I T 4R I sin ( ) (1 ) 2 1 sin ( ) (1 R) 2 2 I 0 0 2 R 4 R 2 I R 1 sin ( ) 4R 2 2 (1 2 R) 2 4 nh 2 cosi 为相位, R 为反射镜的反射率 (b) Reflectiv vity 1.0 0.9 0.8 0.7 Transmis ssivity N=5 N=10 N=15 N=20 N=25 1.45 1.50 1.55 1.60 1.65 Wavelength (µm) 0-10 -20-30 -40 1.52 1.545 1.57 1.595 1.62 Wavelength (µm)
Application: Reflectors/AWG Bragg Grating Reflector K. Okamoto, et al. Opt. Lett., 38(18), 3530-3532 (2013).
Application: Reflectors/Triplexer ITU G.983 standard 1310 nm for Voice&Data 100 nm 1490 nm for Voice&Data 10 nm 1550 nm for Video 20 nm
Application: Reflectors/Triplexer @1310 nm >92% @1490 nm <0.6% N. Zhu, et al. Proc. of SPIE, Vol. 7630 76300W-4
Application: Reflectors/Triplexer Low Index Contrast PLC: SiO 2 /Ge:SiO 2 J. Song, et al. IEEE PTL, 17(12): 2607-2609, (2005).
Application: Grating Coupler 光栅的各次谐波传播常数 v2 v 0 ( v 0, 1, 2,...) 无光栅时导波模传播常数 光栅周期 v 2 相位匹配条件 : k 0 sin i v 0 选择合适的入射角, 自由空间光束耦合进光栅某个谐波, 进而耦合成为光栅导波模 2013/10/13 第二章平面介质光波导和耦合模理论 26
Application: Grating Coupler single-mode fibre, 10 grating adiabatic taper (>150µm) TE 10µm wide waveguide wafer level testing no delicate chip facets very good alignment tolerance efficiency: 30-90% new packaging options
Application: Grating Coupler Experimental results ( =630nm,depth=70nm, TE pol.) 31 % efficiency (5.1 db coupling loss) for very simple design 40nm 1dB bandwidth shallow grating W. Bogaerts, et al. Opt. Express. 12, 1583-1591 (2004) deep trench
Application: Grating Coupler F. Van Laere, et al. J. Lightwave Technol. 25, 151-156 (2007)
Application: Grating Coupler Apodization to match the diffracted mode profile with the fiber mode profile Engineer coupling strength by tuning the fill factor to reduce the amount of diffracted light in the initial periods of the grating and increase the diffracted light at the center of the mode X. Chen et al. IEEE Photon. Technol. Lett., 22, 1156-1158 (2010).
Application: Grating Coupler
Application: Sensing I 入射光谱 I 出射光谱 折射率变化引起 Bragg 波长的偏移 宽谱光源 λ 3dB 耦合器 I Waveguide Grating λ B 光谱仪 λ 反射光谱 折射率变化引起 光谱仪 Bragg 波长的偏移 λ B 波导光栅将外界参量的变化转化为 Bragg 波长的偏移, 通过监测 Bragg 波长的偏移实现对外界参量变化情况的监控 反射光谱和透射光谱之间具有互补性, 因此检测 Bragg 波长的偏移量 λ B 既可以通过监测反射光谱的变化来完成, 也可以通过监测透射光谱的变化来完成, 此方案可以提高光功率的利用率 在光源功率不大, 反射率又不高的情况下, 透射光谱监测方式可以提高测量系统的信噪比 λ
Application: Sensing Y. Fang, et al. Biophysical Journal, 91:1925-1940, (2006).
Application: Sensing P. Dumais, et al. IEEE Sensor Journal, 8(5): 457-464,(2008).
Fabrication- Two beam Interference KrF Excimer laser @248 nm SHG Ar-Ion laser @244 nm
Fabrication- Two beam Interference SiO2 Ge:SiO2 SiO2 Si Substrate UV induced n Effective refractive index against fluence Writing spot diameter Average power density Translation velocity
Fabrication- Two beam Interference The period of each grating g structure was defined through software control with the intersection angle of the two writing beams remaining constant. Demonstration of centre-wavelength detuning applied to direct grating writing
Apodized Grating The duty cycle determines the local modulation contrast of the grating, g, with 100% duty cycle providing the strongest refractive index change C. Sima, et al. Opt. Express. 21, 15747-15754 (2013) uniform grating Gaussian apodized grating sinc-apodized grating
Fabrication- Standard Micro/Nano Fabrication Direct Pattern Transfer Lift-off Pattern Transfer
Fabrication- Nano-Imprinting PDMS Stamp Quartz Stamp
How to measure the reflection spectrum? Transmission 3dB Coupler Waveguide Bragg Grating Input Reflection
How to measure the reflection spectrum?
Summary Principles of Waveguide Bragg Grating Coupled Mode Theory; Bragg Condition Applications: DBR/DFB lasers; Reflectors; Filters; Grating Couplers; Sensors; Fabrication: Two beam interference; Standard Micro/Nano Fabrication; Nano-Imprinting;
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